Antiperspirants combat axillary odors by inhibiting perspiration through the action of astringent salts such as aluminum and zinc salts, but may be irritating to a large number of users. Deodorants function by neutralizing the objectionable odors resulting from the degradation of several components of perspiration by chemical and microbial action into malodorous fatty acids.
Numerous solid antiperspirant and/or deodorant compositions have been described in the chemical and cosmetic literature. These compositions generally are emulsion sticks or suspensoid sticks. Emulsion sticks contain a solution of the antiperspirant ingredient incorporated into the stick via an emulsion. Although emulsion sticks are desirable in certain respects, they tend to be unstable, exhibit tackiness, and leave a visible residue on the skin after use. Suspensoid sticks contain the powdered antiperspirant ingredient suspended in the stick without the use of water or an emulsion. While suspensoids have stability, they tend to leave a white chalky residue on the skin after application.
Manufacturers have found that anhydrous antiperspirant stick systems are more marketable and have good consumer acceptance primarily due to the ease of application to the skin, good cosmetic esthetics and an acceptable degree of effectiveness. Previous to the development of anhydrous stick systems, numerous water based systems were developed in which the active astringent salts were solubilized in a thickened or gelled composition. This is exemplified in U.S. Pat. Nos. 2,732,327; 2,857,315; 3,255,082; and 3,928,557. The water based systems are difficult to apply to the skin, and their consistency and effectiveness are variable.
Many anhydrous stick compositions have been described in the literature which attempt to improve the delivery and the effectiveness of their antiperspirant and deodorant characteristics. Antiperspirant stick systems consisting of low molecular weight monohydric alcohols in conjunction with polyhydric alcohols are described in U.S. Pat. No. 4,137,306. These sticks have the advantage of quicker drying rates, but the residue of the polyhydric alcohols in combination with the astringent salts produces a high degree of tack, and their effectiveness is limited to the type and amount of astringent salts that could be incorporated in the stick matrix.
Anhydrous stick compositions that suspend the aluminum salt in a hydrophobic matrix are described in U.S. Pat. No. 4,049,792. These compositions employ waxy materials and long chain fatty esters to form a stick that delivers the active astringent salts to the skin.
Cosmetic stick compositions made in accordance with these embodiments are greasy, and the active astringent salt is enveloped in a manner that prevents maximum performance. To alleviate this inherent negative characteristic, volatile silicone fluids replacement of the less volatile long chain fatty esters is described in U.S. Pat. No. 4,126,679. This disclosure teaches the advantage of utilizing a volatile non-staining liquid such as cyclic dimethylpolysiloxanes (referred to as volatile silicones), in combination with various types of waxes, as a carrier for the active astringent salts in an antiperspirant stick composition. Similar antiperspirant stick compositions containing volatile silicones are described in U.S. Pat. Nos. 4,511,554; 4,980,156; and 4,985,238.
With respect to deodorant activity, sodium bicarbonate has long been recognized for its deodorant properties, and has commonly been used as a household deodorant. Plain powdered sodium bicarbonate, or sodium bicarbonate diluted with talc or other filler, has been used as an underarm deodorant as disclosed in U.S. Pat. No. 4,382,079. Other publications which describe cosmetic stick compositions containing a bicarbonate deodorant include U.S. Pat. Nos. 4,822,602 and 4,832,945.
However, the development of a practical and effective antiperspirant composition in cosmetic stick form which is also capable of deodorization, and which is capable of consumer acceptability, presents many factors which are unique. Because sodium and potassium bicarbonate have only limited solubility in water, alcohol and other solvents, the preparation of a composition suitable for dispensing in cosmetic stick form has involved many processing obstacles. In addition to the problem of limited solubility, sodium bicarbonate is incompatible with the active astringent salts and with other ingredients of conventional stick compositions. Also, the dimensional stability of the cosmetic stick containing sodium bicarbonate, and the esthetic appearance and the "feel" on the skin, are just a few of the additional difficulties encountered in the preparation of a low residue antiperspirant-deodorant cosmetic stick product.
Another problem associated with the incorporation of a bicarbonate deodorant ingredient in an antiperspirant formulation is the tendency for the high density bicarbonate salt particles to settle in the fluid medium during processing. Also, under the elevated temperature conditions required for the admixing and blending of ingredients, bicarbonate degradation and evolution of carbon dioxide and water occur.
There is continuing interest in the development of antiperspirant cosmetic stick products which exhibit deodorizing activity, and in improved processes for their preparation.
Accordingly, it is an object of this invention to provide a process for the manufacture of an antiperspirant-deodorant cosmetic stick product which contains a bicarbonate deodorant ingredient, and which is characterized by excellent esthetics and cosmetic properties.
It is another object of this invention to provide a homogeneous antiperspirant cosmetic stick product containing a bicarbonate deodorant ingredient which is a particulate solid having particles with an organic polymeric coating that lowers the relative density of the particles.
Other objects and advantages of the present invention shall become apparent from the accompanying description and examples.